I. Field of the Invention
The present invention pertains generally to pneumatic valves. More particularly the present invention pertains to a valve system for mixing a fuel propellant and oxidizer in the injector housing of a rocket engine.
II. Discussion of the Background
In conventional engines, mass flow control is typically accomplished in one of three ways. The first approach utilizes throttling valves that are positioned upstream of the propellant supply manifold. Although this approach is the simplest to implement, high throttling ratios (maximum mass flow rate divided by minimum mass flow rate) cannot be achieved without a significant loss in engine performance. The losses occur because the minimum allowed pressure drop across the injection orifices is not maintained at the entrance to the orifice. The only way to overcome this loss is with a configuration that closely couples the throttling mechanism to the injection orifice.
The second approach is to close couple the throttling mechanism to the injection orifice. With this approach, the propellant manifold is breached and either an electrical or pneumatic actuator is used to drive the mechanism via a mechanical link that passes through this breach. The drawback to this approach is that the breach requires a complex sealing system at the manifold-to-mechanical link interface, which gives rise to reliability issues.
The third approach is a throttling technique known as SLAMMITT (Sliding Action Magneto Mechanical Injector Throttling Technique) which is taught in U.S. Pat. No. 7,257,939 which is herein incorporated by reference. This technique achieves close coupling of the throttling mechanism to the injector orifices. No breach in the propellant manifolds is required since an electric motor is used to drive the throttling assembly. A drawback to this approach concerns the sealing and assembly of the hardware. The assembly is tedious and once assembled the integrity of the seals and throttling hardware cannot be verified.
All of the above prior art techniques concern systems where the fuel manifold is coupled to the combustion chamber. This poses a problem when the engine is fired for extended periods of time, or pulsed on and off multiple times. These actions can cause heat buildup in the combustion chamber walls. If the manifolds share a common wall with the combustion chamber, the unburned, yet reactive, propellants can absorb heat from the combustion chamber and react in the manifolds, causing catastrophic destruction of the engine.